Coating protection of metal surfaces during casting



June 1965 F. J. WEBBERE 3,

COATING PROTECTION OF METAL SURFACES DURING CASTING Original Filed D90.29, 1958 INVENTOR.

ATTORNEY United States Patent 3,191,252 COATING PROTECTION OF METALSURFACES DURING CASTING Fred J. Webbere, Commerce, Mich., assignor toGeneral Motors Corporation, Detroit, Mich., a corporation of DelawareOriginal application Dec. 29, 1958, Ser. No. 783,370, new Patent No.3,045,301, dated July 24, 1962. Divided and this application Dec. 18,1961, Ser. No. 159,847

7 Claims. (Cl. 22-2165) The present application is a division of mycopending United States application, Serial No. 783,370, filed Deinserton contact.

cember 29, 1958, issued as Patent No. 3,045,301, granted July 24, 1962and is owned by the assignee of the instant patent application.

This invention relates to an expansion joint for a member of a thermaldevice having a limited surface portion thereon subjected to rapid andextreme cyclic changes of surface temperature and a method of formingsame. More particularly, the invention pertains to a method of makingarticles which have surfaces that are subject to severe cyclic thermalexpansive and contractive conditions relative to the other surface andinterior portions of the article, such as in internal combustion enginesand the like.

The various surfaces defining a combustion chamber or cylinder of aninternal combustion engine are subjected to rather severe cyclic thermalconditions due to the extremely rapid changes in temperature alternatelyimposed on these surfaces by the heats of compression and combustion andby the flow of relatively cool, gaseous charges into the cylindersduring the engine operating cycle. These changes in surface temperatureresult in the cyclic composition of expansive, compressive andcontractive, tensive stresses on these surfaces and the immediatelyadjacent layers of the various cylinder-defining members. In time thesecyclic stresses result in fatigue cracking of these surfaces. Suchcracking generally occurs intermediate and adjacent ports or openings insuch members where the surface layer subjected to such cyclic stressingis of reduced dimension. Such cracking is also particularly prevalent inthose applications where the engine is subjected to excessivefluctuations in load and speed; factors which result in suddenapplications of relatively cool, incoming air onto overheatedcylinder-defining surfaces.

This invention contemplates providing the combustion chamber surfaces ofa thermal device of the type described with expansion joints similar infunction to those shown and described in United States patentapplication Serial No. 650,249, now United States Patent No. 2,893,371,filed April 2, 1957, in the name of Vernon E. Schafer, Jr., entitledExpansion Joint and which is assigned to the assignee of the presentinvention. Such expansion joints are formed by casting metal insertswhich are coated with a fusion-inhibiting material into thecylinder-defiining members adjacent critical areas. These insertsintersect the combustion chamber surface and extend through the layer ofthe member normally subjected to such cyclic expansive and contractivethermal conditions. Under engine operating conditions, the initialexpansive compression imposed on this surface layer stresses this layerbeyond its compressive yield point. for the temperatures "ice involvedand affects the formation of grooves immediately adjacent to andincluding the opposite sides of the insert. These grooves serve toaccommodate and isolate subsequent expansion and contraction of thesurface layer from the adjacent critical areas.

In casting steel inserts in a cast iron engine cylinder head for theabove purpose, the carbon in the molten cast iron has a tendency todiffuse into the metal of the This diffusion of carbon changes thecharacteristics of the steel whereupon the insert has a tendency to meltand fuse with the cast iron, destroying the intended beneficial elfectsof individuality.

Accordingly, it is a primary object of my invention to provide a rapidand economical means to prevent this diffusion and to provide a methodof economically casting a steel insert in a cast iron cylinder head soas to retain individuality of the insert.

Other objects, features and advantages of the present invention willbecome more apparent from the following description of preferredembodiments thereof and from the drawing, in which:

FIGURE 1 is a fragmentary sectional view of the exhaust port area in thecylinder head of an internal combustion engine of the uniflow,two-cycle, diesel type;

FIGURE 2 is a perspective view of one form of insert shown in FIGURE 1;

FIGURE 3 is a perspective view of a second form of insert, such as shownin FIGURE v1;

FIGURE 3a is an enlarged fragmentary sectional view of FIGURE 3; and

FIGURE 4 is a perspective view of a modified form of insert adapted foruse in place of the insert shown in FIGURE 3.

Referring more particularly to the drawing, FIGURE 1 shows a portion ofa cylinder head 10 of a uniflow, twocycle, diesel engine. Each cylinderin the engine is provided with two exhaust passages 12 which arerespectively connected to exhaust ports 14 which flank an opening (notshown) provided in the head for the nozzle of a fuel injector. The outerperiphery 16 of the exhaust ports 14 is beveled to seat the heads of twoexhaust valves (not shown) which are reciprocably mounted in the head.As indicated above, the combustion chamber or fire deck surface 18 ofthe cylinder head of such an engine is particularly susceptible tosurface cracking intermediate and adjacent the valve ports and injectornozzle opening. The cracking which occurs intermediate the injectoropenand the exhaust ports is generally in a diametrical plane common tothe several openings. The expansion and contraction of the fire decksurface parallel to this common diametrical plane also tends to developsunbursttype cracking of the fire deck surface radially outwardly fromthe exhaust ports transversely of this common diametrical plane.

As shown in FIGURE 1, inserts 20 and 22 are cast into the cylinder headin accordance with the invention and serve to isolate the cyclicexpansion and contraction of the combustion chamber surface from thecritical areas intermediate and adjacent to the injector opening, thevalve ports and other openings through the fire deck of the cylinderhead. These inserts are of limited mass to prevent chilling duringcasting and, as shown in FIGURE 3a, have a coating 23 to prevent fusionof the insert with the molten metal during the casting process.

In the illustrative embodiments,

face-layer of the fire deck which defines the combustion. v

chamber and is subjected to the the cyclic'thcrmal conditions. Thecorrugations in the inserts extendparallel to the combustion chambersurface and interlock with the adjacent surfaces of the cylinder head.By using such corrugations, it has-been found that such inserts can beused without increasing. thethickness of the fire'deck in asmuch astheinterlocking, serrated surfaces carry the, compression and combustionloads imposed on the ,adjacent portions of the firedeck.

' The inserts and 22 are terminated inwardl-yof. the

fire deck from their corrugated portions by-rounded or cylindricallylooped portions28. These looped portions are open lengthwise to permitthe free flow of molten metal within the loop during the casting processand serve to terminate the cracks formed in the head by the use .of suchinserts. portion 28 which extends in parallel spaced relation to thecombustion chamber surface and intersects the coun The inserts 22 eachhave a single .looped' ter bores for the valve seat inserts at itsopposite .end.

The inserts 20 are each rounded to provide two cylindrical or loopedportions 28 and 30 formed at right angles to each other. The'loopedportion 30 is normal to and intersects the combustion chamber surface atone end,

and the looped portion 28 extends in parallel spaced relar tion to thecombustion chamber surface and, intersects the adjacent valve port 14atits end opposite the looped portion. 30.

Under normal engine-operating conditions, the cyclic expansion of thesurface layer of the head adjacent-the combustion chamber affects theformation of-narrow grooves (not shown) and in the surface of thecasting i-m= 1 mediately adjacent the inserts 20 and 22, respectively;Since the compressive stresses resulting from such cyclic expansionexceed the yield points of the insert and head materials at thetemperaturesinvolved, these grooves are formed in part by the outwardextrusion. of a portion of the insert and in part by the permanentupsetting of the adjacent surface layer. The grooves are thus .formedduring the initial or breaking-in period of engine operation to thedepth of this surface layer subjected to cyclicthermal conditions-andare adapted to accommodate subse quent expansive and contractiye plasticflow of this surface layer without' imposing further compressive andtensive stresseson the critical areas of the head intermediatetheinserts. A third form of insert 32 is shown in FIGURE 4. Thisinsertis generally triangular in shape and particularly 'de signed for use inapplications similar to that for which the inserts 20 and 22 are used inthe above described em? bodiment. As shownQt-he insert 32 has a portion34 cor- 'rier and do not readily settle out.

forma coating having a thickness of at least 0.0005 inch by spraying,dipping, rolling, brushing, or the like. The maximum thickness of acoating which can be used is dependent upon the particular applicationand, in general, a. variety. of coating thicknesses above about 0.0005inch can be used. The thickness of the coating generally is limited onlyby that thickness which will tend to impair surface detail on theinsert, but in some instances exceedingly heavy deposits may tend to bechipped off readily in handling and are, therefore, undesirable. Coatingthicknessesof approximately 0.0005 inch to 0.0015 inch can be usedformost applications without impairing 'surface detail. 7

After the coating is applied, it is dried so that the insert can bereadilyhandle'd prior to the casting operation without detrimentallyaffecting the coating, such as by scratching, nicking, etc. Although thecoating can be dried at room temperature, it is preferred to acceleratethe drying .by heating at elevated temperatures. When using a suitablesilicone resin or tributyltitanate as the carrier, the

. coating is preferably dried at temperatures from about 200 F. to 500?F. for about 10-to 20 minutes.

I: have found that successful results are obtained when using a mixturecontaining approximately 20% to 40%,

by weight, aluminum or aluminum base alloys and levigated alumina inamounts from approximately 5% to 1.0%, by weight. In some instances,amounts of alumina as high as approximately 20%, by weight, arepreferred.- ln referring to aluminum basealloys, I intend to encompassalloys containing at least about 80% aluminum.

The particle size of the aluminum or aluminum base alloys, as well asthe alumina are preferably of such a size that they can be readilydispersed in a suitable car- Generally, I prefer to .use particle. sizesof at least about 2 microns since particles of smaller size tend t oform aggregates which are not readily broken. during the mixing, thusinhibiting dispersion of the individual particles in the carrier.

Generally, aluminum or aluminum base alloys. which have a particle sizethat will pass through a standard 400 mesh screen but which have anaverage minimum mean diameter of about 2 micronscan be used. Particlesizes of thealuminum or aluminum base alloysin excess of about. 400 meshtend'to beexceedingly inefiicient in maintaining separation of thealuminum particles and are .quite difficult to maintain in uniformdispersion. Such particles tend to settle out quite rapidly from themixture.

Since .the aluminais quite important in preventing the wetting of thesurface of the insert'by .themolten casting metal, it is important thatthe size of the alumina particles be maintained fairly small... I havefound that levigated alumina having particle sizes of approximately 2microns to 10, microns provide generally satisfactory results.

a The carrier for the alumina and aluminum base alloys .or aluminumwhich .is to be used can be of any type which will functiontsatsfactorily in the given application. The

respondingto the portion 24 of insert 20 and having cor rugationsintended to provide interlocking surfaces parallel to the combustionchamber surface of the fire deck. A rounded bead 36 is formed arcuatelyvand generally diagonally of theco-rrugations and is adapted to terminatethe insert created crack; intersecting theexhaust port 14 at one end.and the surface 18 ofthe combustion chamber at its other end. 1 Y 7 a 1a In accordance with-my invention, the formed insert is coated with amixture of powdered aluminum or a powdered aluminum 'base alloy,levigated, or powdered, alumina and .a carrier, which preferablyfunctions :as a binder.

A suflicient .quantity. of :the coatingmixture isapplied to adhesivecharacteristics. 7 have been obtained using tributyltitanate andpolyorgano-' carrier preferably acts as a binder for the particles,making themv adhere to the surface'of the insert. In someinstances,f,the carrier can befcomposed of binder plus a volatilesolvent which is used to'thin the mixture. Although a binder isgenerally preferred for the carrier, in

some instances the carrier can be only'avolatile solvent.

However, in instances where the inserts must be handled to someextentbefore the casting operation and in which handling .the partsmaybe subjected to some abuse, it is essentially desirable "that thealuminum and aluminum oxide be supported in a carrier whichhas bondingor Especially satisfactory results siloxanes as carriers which havebonding char'ac'te-ristics. Alkyl-a rylandl dialkyl polyorganosiloxanes,such as a phenyl methyl polysilo'xane or a dimethyl polysiloxane, eachhaving a molecular Weight in the nature of about 1400 to 1600, isgenerally useful. a 1

' Volatile solvents, such as acetone, alcohol, methyl ethyl ketone, canbe used to thin the mixture so that it can be handled more readily. Whenusing tributyltitanate as a binder, however, extreme care must beemployed to avoid using a thinner which has excessive moisture thereinsince mixture of such a thinner with tributyltitanate tends to decomposethe tributyltitanate.

As a specific example of my invention inserts, such as hereinbeforedescribed, made of SAE 1008 steel can be cast in a uniflow, two-cycle,diesel engine cylinder head having a composition which is as follows,all percentages by weight:

Carbon 3.25% to 3.50%. Silicon 2.0% to 2.5%. Manganese 0.4% to 0.8%.Sulfur 0.1% Maximum. Phosphorus 0.05% Maximum. Chromium 0.3% Maximum.Nickel 0.3% Maximum. Iron Balance.

An insert of SAE 1008 steel which is placed in contact with a moltencast iron alloy, such as described above, readily absorbs carbon fromthe molten alloy. The melting point of the steel is reduced to such anextent that the steel insert is melted and blends with the cast iron,destroying the individuality of the insert necessary to obtain thebenefits of the invention.

However, I have found that such action was eliminated by dipping theinsert into a liquid mixture containing milliliters of tributyltitanate,15 grams aluminum powder and 3 grams levigated alumina. After dippingthe part in the mixture, the part was shaken vigorously to removeexcessive amounts of the coating mixture and subsequently dried for 15minutes at approximately 300 F. The part was subsequentily located in acylinder head mold in spaced relationship to form the cylinder headpreviously described. Generally, any type of mold can be used which issuitable for the casting of cylinder heads without inserts. The insertsare maintained in position in the mold in the normal and accepted mannerfor casting inserts. Typically, the mold cavity surface can be groovedand the inserts placed therein. With the inserts in the mold, the moltencast iron is introduced to form the cylinder head.

After the casting operation, the mold members were removed in aconventional manner leaving the resultant head casting accessible forfurther treatment. The casting was then cleaned and subsequentlymachined in the usual manner to the finished fire deck surface and valveports, as shown in FIGURE 1. These machining operations, of course,insure that the inserts properly intersect the finished surfaces of thehead.

In some instances this invention is preferred for casting other types ofsteel inserts. in cast iron articles. This invention has been especiallysatisfactory in forming cast iron castings which have exceedinglycomplex passages therein. Finished castings of this type are frequentlynot easily made using conventional coring techniques. In such instances,it may be desirable to coat, in a manner such as herein described, theexterior of a tubular member which is preformed to the desired contourof the passage in the casting. The coated, preformed tubing is thensuitably located in a mold and the molten casting metal introduced. Inthis maner highly satisfactory results are obtained which cannot bereadily obtained by conventional coring methods.

It is also contemplated that, in some instances, the subject mixture isespecially satisfactory when used as a core wash in the known andaccepted manner. Under some circumstances it is desirable to coat themold cavitydefining surface of a chill in a mold. In such event thesubject type mixture provides an especially satisfactory coating whichinhibits wetting of the chill and diffusion across the interface betweenthe chill and the molten casting metal.

' Although this invention has been described in connection with certainspecific examples thereof, no limitation is intended thereby except asdefined in the appended claims.

I claim:

1. A method of casting which comprises applying a coating to a surfaceof a part which is to be in contact with a molten metal, said coatingcomprising, by Weight, about 20% to 40% of a powdered metal from thegroup consisting of aluminum and aluminum base alloys, 5% to 20% oflevigated alumina and about 40% to 75% of a carrier from the groupconsisting of polyorganosiloxanes and tributyltitanate, said metalhaving a particle size of from about 400 mesh to about 2 microns, saidalumina having a particle size of approximately 2 microns to 10 microns,drying said coating and casting molten metal against the surface of saidpart.

2. The method described in claim 1 in which the carrier istributyltitanate.

3. A method of casting which comprises applying a coating having athickness of at least 0.0005 inch to a surface of a part which is to bein contact with a molten metal, said coating comprising, by weight,about 20% to 40% of a powdered metal from the group consisting ofaluminum and aluminum base alloys, 5% to 20% of levigated alumina andabout 40% to 75% of a carrier from the group consisting of phenyl methylpolysiloxane, dimethyl siloxane and tributyltitanate, drying saidcoating and casting molten metal against the surface of said part.

4. A method of casting which comprises coating a surface of a part witha mixture which comprises approximately, by weight, about 20% to 40% ofa powdered metal from the group consisting of aluminum and aluminum basealloys, about 5% to 20% levigated alumina and about 40% to 75% of abinder to form a coating having a thickness of at least 0.0005 inch,said metal having a particle size of from about 400 mesh toapproximately 2 microns, drying said coating, placing said part in amold and introducing molten metal into said mold so as to be in contactwith said coated surface.

5. A method of casting which comprises coating a surface of a part witha mixture which comprises approximately, by weight, about 20% to 40% ofa powdered metal from the group consisting of aluminum and aluminum basealloys, about 5% to 20% levigated alumina and about 40% to 75tributyltitanate to form a coating having a thickness of at least 0.0005inch, said metal having a particle size of from approximately 400 meshto about 2 microns, said aluminum having a particle size of about 2microns to 10 microns, drying said coating, placing said part in a moldand introducing molten metal into said mold so as to be in contact withsaid coated surface.

6. A method of casting which comprises coating a part with a mixturewhich comprises approximately, by weight, about 20% to 40% of a powderedmetal from the group consisting of aluminum and aluminum base alloys,about 5% to 20% levigated alumina and about 40% to 75 of a carrier fromthe group consisting of phenyl methyl siloxane, dimethyl siloxane andtributyltitanate to form a coating having a thickness of about 0.0005inch to 0.0015 inch, said metal having a particle size of fromapproximately 400 mesh to about 2 microns, said alumina having aparticle size of about 2 microns to 10 microns, drying said coating,placing said part in a mold and introducing molten metal into said moldso as to be in contact with said coated surface.

7. A method of casting which comprises coating a cylinder head moldsteel insert with a mixture which comprises approximately, by weight,about 20% to 40% of a powdered metal having a particle size of fromapproximately 400 mesh to about 2 microns from the group consisting ofaluminum and aluminum base alloys, about 5% to 20% levigated aluminahaving a particle size of 7 '8" about 2 microns to 10 microns, andahotit 40% to 75% 2,872,715 2/59 Bean 224-202 of a binder to form acoating having a thickness of at 2,875,485 3/59 Schneider 22-1931east.0.0 005 inch, drying said coating, placing said part 2,903,375,9/59 Peras 117-53 in a cylinder head mold and introducing molten castiron 2,975,494 a 3/61 C b 1 06 38 35 into said mold so as to cast saidmolten cast iron around .5

said coated insert.

References Cited by the Examiner V V V I UNITED STATES PATENTS 7 MICHAELV. BRINDISI, PrimaryrExamine r. 2503068 5/50 Undfirwotfl 117-4543 10MARCUSU.LYONS, Examin'er. 2,599,185 6/52 Lepp'et a1. 106-65 FOREIGNPATENTS, 584,160 1/47 Great Britain.

7. A METHOD OF CASTING WHICH COMPRISES COATING A CYLINDER HEAD MOLDSTEEL INSERT WITH A MIXTURE WHICH COMPRISES APPROXIMATELY, BY WEIGHT,ABOUT 20% TO 40% OF A POWDERED METAL HAVING A PARTICLE SIZE OF FROMAPPROXIMATELY 400 MESH TO ABOUT 2 MICRONS FROM THE GROUP CONSISTING OFALUMINUM AND ALUMINUM BASE ALLOYS, ABOUT 5% TO 20% LEVIGATED ALUMINAHAVING A PARTICLE SIZE OF ABOUT 2 MICRONS TO 10 MICRONS, AND ABOUT 40%TO 75% OF A BINDER TO FORM A COATINF HAVING A THICKNESS OF AT LEAST0.0005 INCH, DRYING SAID COATING, PLACING SAID PART IN A CYLINDER HEADMOLD AND INTRODUCING MOLTEN CAST IRON INTO SAID MOLD SO AS TO CAST SAIDMOLTEN CAST IRON AROUND SAID COATED INSERT.